Using a different offset from 1 in the function LEAD does not seem to work.

Question

Hi,
I have the following rows in a table:
SQL> select job_id from jw_exception_accesses
2 where rownum < 11
3 order by job_id;
JOB_ID
442484177
443178279
443178279
443357232
443443617
443536258
1. When I try and use the offset of 2 with the LEAD function, it brings back nothing.
SQL> select job_id,lead(job_id,2) over (order by job_id) as next_job
2 from jw_exception_accesses
3 order by job_id;
JOB_ID NEXT_JOB
442484177
2. When I try and use the offset of 1 with the LEAD function, with rownum, it
brings back nothing:
SQL> select job_id,lead(job_id,1) over (order by job_id) as next_job
2 from jw_exception_accesses
3 where rownum < 2;
JOB_ID NEXT_JOB
443618290
3. When I try and use the LEAD function with a particular row as the current row,
it brings back nothing:
SQL> select job_id,lead(job_id,2) over (order by job_id) as next_job
2 from jw_exception_accesses
3 where job_id = 421624348;
JOB_ID NEXT_JOB
421624348
4. When I try and use the MIN function, to just get one row back, it brings
nothing back.
SQL> select min(job_id),lead(min(job_id),1) over (order by min(job_id)) as next_job
2 from jw_exception_accesses;
MIN(JOB_ID) NEXT_JOB
421624348
OR
SQL> select min(job_id),lead(job_id,1) over (order by job_id) as next_job
2 from jw_exception_accesses
3 where rownum < 2
4 group by job_id;
MIN(JOB_ID) NEXT_JOB
443618290
And yet manuals say you can use a particular row as the launching row.
Any ideas anyone?
Thanks very much for any help.
- J

Answer 1

Hi,
user1636556 wrote:
... 1. When I try and use the offset of 2 with the LEAD function, it brings back nothing.
SQL> select job_id,lead(job_id,2) over (order by job_id) as next_job
2 from jw_exception_accesses
3 order by job_id;
JOB_ID NEXT_JOB
442484177
MIN(JOB_ID) NEXT_JOB
443618290It works fine for me:
SELECT       ename
,       LEAD (ename, 2) OVER (ORDER BY ename)     AS lead_2
FROM        scott.emp
ORDER BY  ename
;Ouptut:
ENAME      LEAD_2
ADAMS      BLAKE
ALLEN      CLARK
BLAKE      FORD
CLARK      JAMES
FORD       JONES
JAMES      KING
JONES      MARTIN
KING       MILLER
MARTIN     SCOTT
MILLER     SMITH
SCOTT      TURNER
SMITH      WARD
TURNER
WARDNotice that LEAD does return NULL near the ned of the result set, when there are not 2 later rows.
Post a complete test script that people can run to re-create your problem. Include CREATE TABLE and INSERT statements for your tables (unless you're using commonly available tables, like those in the scott or hr schemas).
Post the results you want to get from that data.
2. When I try and use the offset of 1 with the LEAD function, with rownum, it
brings back nothing:
SQL> select job_id,lead(job_id,1) over (order by job_id) as next_job
2 from jw_exception_accesses
3 where rownum < 2;
JOB_ID NEXT_JOB
443618290
3. When I try and use the LEAD function with a particular row as the current row,
it brings back nothing:
SQL> select job_id,lead(job_id,2) over (order by job_id) as next_job
2 from jw_exception_accesses
3 where job_id = 421624348;
JOB_ID NEXT_JOB
421624348
4. When I try and use the MIN function, to just get one row back, it brings
nothing back.
SQL> select min(job_id),lead(min(job_id),1) over (order by min(job_id)) as next_job
2 from jw_exception_accesses;
MIN(JOB_ID) NEXT_JOB
421624348
OR
SQL> select min(job_id),lead(job_id,1) over (order by job_id) as next_job
2 from jw_exception_accesses
3 where rownum < 2
4 group by job_id;Analytic functions are computed after the WHERE clause is applied. If the WHERE clause narrows the result set down to n rows, then LEAD (x, n) will always return NULL.
Analytic functions are computed after the GROUP BY clause, too, so you can use analytic functions in a GROUP BY query, but only using expressions that would be legal in the SELECT clause (aggregates, the GROUP BY columns, and constants).